Sunday, May 31, 2009

What Is An SPG ?

First off the SPG stands for Submersible Pressure Guage. SPGs let divers monitor their air supply (pressure) throughout the course of the dive. Such guages connect to the high pressure port on the regulator's first stage. Click on picture to take you to Leisure Pro Equipment.

You will learn to use the SPG to plan and control your dive so you return safely to the boat or shore without running out of air. The SPG is considered mandatory equipment when you dive, that is if you do not dive with a computer. Depending on the dive and type of dive, some divers dive with both an SPG and computer. The SPG of course is th back up.

A vital point to remember, that the SPG is a passive device. You have to read it, or it doesn't do any good. Develop the habit of looking at it frequently through out out the dive. When you dive alot you can get the feel of how fast you breathe air, and know about when you are to run out. So you may not need to check that often. But for the new divers, I recommend checking it often. Better too much than too little.

The most common type is an analog model with a spiral wound bourbon tube. Europeans SPGs go to 300 bar, while in North America SPGs range from 3500 - 4000 psi. On the dial the SPGs are color coded. In Europe for 0-35-70 bar and North America 500- 000 psi. The color is usually red and warns that you are dangerous low on air and need to return to surface immediately.

Wednesday, May 27, 2009

How to Determine the Proper Amount of Weight Needed for the Dive

Divers take the weight belt and systems for granted more than they should.
This is the system that allows them to have a safe and comfortable dive. Too much weight and you are always struggling to maintain buoynancy, too little weight and the descent to start the dive will be difficult.


Before going on the first dive, we teach divers to do the weight and buoyancy test. This is how the test is performed. You will have to enlist the help of other divers to help with this test. You will start off with some weight in the BCD. Thew dive shop or instructor will give you a basic guide to how much. This depends on a few factors: what type water you are diveing be it salt or fresh water, also how much weight you are. Are you thin, heavy, or in between. Keep in mind that this is a starting weight.

To do the test. You will need to enlist the help of other divers to hand you weight etc.

1. Enter the water with all the gear and your estimated weight. Get in water that is over your head but not far from the exit and shore.

2. Make sure that all the air is out of the BCD. Keep the regulator in your mouth, and hold a NORMAL breath of air. Be ready to kick up if you begin to sink. This is where the help is needed.

4. You should float at eye level. If you do not, add or suntract weight till you are. You can just hold the weights till you figure out how much. Then once you do you can intergrate them into your BCD or Weight belt.

5. As a final check, exhale. You should begin to slowly descend if you have the proper amount of weight. You should also raise the deflator over your head with your left hand. This will also help you decend, because now you are using the weight of you arm to help with this.

6. Once you have dtermined the weight to this point, you will need to add a small amount ot EXTRA weight (about 2 pounds)

Why ? Air has weight. As you use the air in your tank the tank begins to become lighter and more buoyant. Add ting extra weight will off set the buoynacy factor that you get by the end of the dive.


Weight also has a direct effect on how often bouyanct adjustments are made. If the diver carries more weight than needed to "help get underwater better". they also have to add more air to the BCD as they dive to ofset the extra lead weight added on the surface. Now the volume of air exchanges with depth, this causes a greater changes in buoyancy, which causes a diver to adjust the air in their BCDs more often.

Wednesday, May 20, 2009

Factors Predisposing Divers
to Decompression Sickness

As mentioned in the last blog and talkcast, the way to avoid is to limit the factors that predispose divers to DCS. Some factors are unavoidable. So make the others of more importance. Physiologists still don't understand all factors that may predispose an individual to DCS, but the list is a start to what they do know. No matter what you do, DIVE CONSERVATIVELY. NEVER DIVE TO THE LIMITS OF A DIVE TABLE OR COMPUTER. They may be wrong for you at that time.

Following is a short list of these factors and a brief explanation.


Fat tissue is slow tissue, holding a high amount of dissolved nitrogen. A lot of fat tissue increases the nitrogen retained in the body. Divers that have a higher fat ratio to lean muscle are more likely to have more nitrogen after a dive and therefore have a slightly higher risk of DCS.


The circulatory and respiratory system works less efficiently in the older population. This interferes with gas exchange. Remain fit by reducing the fat content and exercising regularly to counter this factor.


Dehydration reduces the quanity (volume) of blood available for gas exchange, slowing nitrogen removal from the body. Comsumption of diuretics (caffine), profuse perspiration, and even the dry scuba air tend to dehydrate the diver. During metabolism of alcohol uses a great deal of water. Thus a diver with a hangover is more likely to be partially dehydrated. To do: Make sure you drink plenty of water before, during and after the dive. More than you normally would do.


Any condition that affects normal circulation can potentially affect nitrogen elimination. Healed conditions may reduce local circulation difficulties. Also any illness can produce a general reduction in circulation. Make sure you do not dive if you have any injuries or illnesses. It is simply not worth it. Better to heal and dive a different day.


Alcohol consumed before or after a dive alters physiology, we all know that but in favor of DCS. Alcohol tends to accelerate circulation and can cause tissues to carry higher amounts of nitrogen. After a dive, alcohol dilates capillaries, possibly increasing the rate of nitrogen release and bubble formation.


Elevated carbon dioxide from skip breathing or improper breathing may interfere with the gas transport by the circulatory system by dilating the capillaries, and again increasing nitrogen uptake.


During a cold dive, inadequate exposure protection in moderately warm water, changes normal circulation, as the body trys to stay warm. At start of dive, circulation carries nitrogen to all parts of the body, but as heat is conserved, this reduces circulation to the hands and feet. There is less blood to carry away dissolved nitrogen during ascent.


Exercise while diving increases blood circulation, carrying nitrogen to all parts of the body faster than normal. After resting, circulation returns to normal, and so there is no corresponding circulation to accelerate nitrogen elimination.


Reduced atmosphere pressure at altitude increases the pressure gradient between tissue and the ambient pressures and can possibly cause larger bubble formation. Once DCS occurs returning to sea level does not usually correct the problem

Sunday, May 17, 2009

The Squeeze is On

What do I mean by this statement ? As divers, we have many areas that can cause us to have equipment squeezes. But one of the main areas that affect most of us as divers is the squeeze that occurs from our face mask.

Unequalized air spaces can create problems. As mention the mask squeeze is common and occurs on very rapid descents when the diver neglects to equalize the mask.
Increasing hydrostatic pressure forces tissues surrounding the eye to swell into the uncompensated air spaces to fill the reduced air volume.

This swelling damages the capillaries, bruising the skin around the eyes and cheeks. Mask squeeze looks dramatic and severe, and the diver may not know it happened until they look in the mirror. This squeeze clears without complications, but the victim may want to consult an MD.

Other squeeze that may occur is when a diver uses a dry suit. If the diver forgets to add air to the suit and ignores the pinching, and continues to descend, may cause welts and injury.

During ascents the diver must remember to release the air from the suit, or risk a possible runaway ascent.

Sunday, May 10, 2009

The Difference Between DCS and DCI

Most divers do not know there is a difference between Decompression Sickness (DCS) and Decompression Illness (DCI). There is a large difference.

First we must define what we mean by DCS. There is an overall term called Decompression Illness (DCI) which most divers get confused and call decompression sickness (DCS), the same. No it is not the same. DCI is the over all term that has 2 subjects below it: 1) DCS and 2) Lung Over expansion Injuries.

DCS refers to the conditions caused by inert nitrogen gas coming out of solution within the body. Lung Over expansion Injuries refer to those injuries that are caused by holding your breath on ascent.

There are basically 2 types of DCS: Type I deal with skin and pain only which would include the sub type a) Cutaneous DCS and b) Joint and limb pain DCS. While Type II covers the more life-threatening which are the c) neurological DCS and d) Pulmonary DCS.


Bubbles coming out of solution in skin capillaries can cause this type.


Bubbles growing around and inside the tendons, ligaments and related muscles are the immediate cause. Symptoms may be found in one place on the same limb or bilateral symptoms. This type may be serious because it can lead to a mores serious problem.


Effects on the nervous system produce some of the more serious cases in DCS. Bubbles in the nervous tissue may block blood flow "backing up" the system and reduce arterial flow in the affected areas. This affects the spinal cord most often often causing numbness and paralysis in the lower legs. It tend creeps upwards to affect from the neck down.


This is DCS that manifesting itself in the lung capillaries resulting in the onset of life-threatening symptoms. Silent bubbles reach the pulmonary capilaries defusing into the alveoli. In some cases, bubbles accumulate faster than they diffuse and can block and back up blood flow to the lungs. With less blood flowing to the lungs, the left side of the heart gets less blood, causing the heart rate to rise and a drop in blood pressure. With no treatment, the circulatory system may fail.

There are four type of Lung Overexpansion Injuries


This is if air enters the bloodstream through a ruptured alveoli into the pulmonary capillaries.


If lung over pressurized tears at the surface, the expanding air leaks between the lung and the peural lining.


This is where air accumulates in the mediastinum.


Follows that of Mediastinal Emphysema as air seeks its way from the mediastinum, foloowing the path of least resistance into the soft tissues at the base of the neck.

Sunday, May 3, 2009

What is the Difference between
Steel and Aluminum Tanks ?

During this blog I am going to explain the differences between a steel tank and an aluminum tank.

There are many pros and cons concerning which tank you dive with, I will try to highlight those differences do when you do decide on buying a set of tanks, you will be better informed. Of course, as always, consult you local dive shop so you can see and touch the tanks you are considering buying. They will be able to fill in the blanks for you concerning which to buy and why. I hope that this information is helpful. Now let's get on with it.

The vast majority of tanks today are either steel or aluminum.


Most are made from chrome-molybdenum steel. Steel cylinders are hard and therefore resistant to external damage. The draw back for steel, without proper care, they may rust (A chemical reaction that forms iron oxide), not only on the outside, but inside as well. One reason to have your tanks visually inspected every year. Highly recommended.


Softer than steel, ie can become damaged for external forces. Because of this, the walls are thicker. This makes them larger, heavier, and more positively buoyant than steel. Like steel aluminum also corrodes forming aluminum oxide. Unlike the iron oxide, it actually inhibits further corrosion.


Aluminum weighs less than steel. Because they are not as strong, tend to be larger and heavier than steel. This can concern the smaller diver.


Because aluminum is larger they displace more water and often times more buoyant. As such divers will need more weight in their belt for a diver. At the end of the dive they tend to be more positively buoyant. Where as steel is negatively buoyant after a dive. The total difference can be 4-8 pounds.


Most steel tanks are considered high pressure tanks, which mean that they may have the plus sign after the tank allowed pressure. This as you remember means that you can fill it up to 10 % higher than what is listed. Most steel tanks have what you call a DIN valve, where the first stage of your regulator screws into the tank. This tends to get a more secure fit. While the aluminum tanks have a K valve, where the first stage just rest against the tank stem, and is held in place by sir pressure.


Steel tanks cost considerably more than aluminum.